Story highlights

The number of births in the US rose 1% in 2014, the first increase since 2007

The reproductive rebound was driven by women in their thirties and forties who may be responding to the economic rebound

The rate of teen births dropped to 24.2 for 1,000 teens, which is an all-time low

(CNN)The number of births in the United States went up last year for the first time since 2007, according to an annual report by the CDC National Center for Health Statistics. The report found that there were 62.9 births for every 1,000 women between the ages of 15 and 44, which represents an increase of 1% over the birth rate in 2013.

The spike was driven by women in their 30s and early 40s, who had 3% and 2% more births, respectively, than in the previous year. For women in their 30s, the birth rates were 100.8 per 1,000 women age 30 to 34 and 50.9 per 1,000 women age 35 to 39. In contrast, the birth rate among teens 15 to 19, which has been waning since 1991, plummeted 9% since 2013. It was 24.2 per 1,000 teens in 2014. The rate among women in their early 20s also dropped by 2%.

"The births to older women was enough to offset the decline in teen birth rate and you see this overall increase," said Brady E. Hamilton, a statistician and demographer at the National Center for Health Statistics and lead author of the study.

"In regards to the older women, this is kind of a continuation of a trend, but the decline in teens 15 to 19 really shocked me; 9% is really phenomenal," Hamilton said.

The birth rate among teens has gone down 61% since 1991. But the rate of decline has picked up speed in the last seven years, dropping 7% annually between 2007 and 2013 and now 9% in the last year.

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The economic downturn that started in 2007 is probably partly responsible for the reproductive downturn among all age groups, including teens, Hamilton said. Now that the economy has improved, older women may be having the births that they postponed several years earlier, he added.

"There seems to be a cultural shift among teens and young adults valuing not getting pregnant," said Laura Lindberg, a principal research scientist at the Guttmacher Institute. Teens and young adults are increasingly able to prevent undesired pregnancies because of improved access to contraceptives and other services, Lindberg added.

The decline has occurred in every racial and socioeconomic group and state, suggesting that the decline is due to a widespread increase in access to services and contraceptives, Lindberg said. "We are likely to see continued decline [among teens and young adults] driven in part by the increased use of IUDs (intrauterine devices)," Lindberg said.

The CDC abortion surveillance indicates that there has not been in increase in abortions among teens, at least since 2011 (the last year that data were available). The trend of fewer teen births is probably not because more teens are having abortions, said Theodore J. Joyce, professor of economics at Baruch College at the City University of New York.

The birth rate for women 30 to 34 and 35 to 39 has been increasing steadily since 2011 and 2010, according to the CDC report. "We are seeing this as sign of the times that people are responding to the end of the recession by being more comfortable in having a child," Lindberg said. However it is not clear if the trend will continue, she added.

The number of births among older women 40 to 44 has been increasing steadily since at least 1990, including over the period from 2007 to 2013. Women in their 40s may not feel like they have the option to postpone pregnancy as much as younger women, said Hamilton, author of the current report.

The overall birth rate increase in 2014 was observed among all races, except for American Indian and Alaska Native women. Hamilton and his colleagues are following up with an in-depth report on birth rates, which will include more information about these two groups as well as different Hispanic groups, such as Mexican and Puerto Rican.

The report also looked at several details of maternal and infant health. It found that the rate of preterm births continued to decrease, to 9.57% in 2014; the rate of low birthweight (newborns weighing less than 5 pounds, 8 ounces) has been on the decline since 2007 and was 8% in 2014.

The rate of cesarean delivery also dropped 2% from 32.7% in 2013 to 32.2% in 2014. "This is the biggest drop in 20 years," said Dr. Aaron B. Caughey, chair of the department of obstetrics and gynecology at Oregon Health & Science University. "Ob gyns have become more conservative about doing cesarean deliveries in the last four or five years because there is a more clear recognition of the risk for the mother both for the current and future pregnancies," said Caughey, who co-authored the American College of Obstetricians and Gynecologists recommendations on cesarean delivery.